In an integrated circuit (IC) chip (hereinafter chip), various signals, such as power supply signals, work mode signals and functional signals, etc., are input to a signal input circuit integrated into the chip through pins of the chip, and transmitted to corresponding signal processing units through the signal input circuit. When the chip performs multiple work modes, multiple work mode signals are needed, and the chip performs various work modes by combining these multiple work mode signals.
In a conventional chip, each work mode signal is input through a separate work mode pin, that is, each work mode signal needs a pin. FIG. 1 shows a block diagram of a conventional signal input circuit. As shown in FIG. 1, the signal input circuit 100 includes multiple work mode signal units 111 through 111J and multiple functional signal units 121 through 121K, where J and K represent positive integers. In other words, the signal input circuit 100 includes at least one work mode signal unit and at least one functional signal unit. Each input terminal of the work mode signal units 111 through 11J is used as a work mode signal input terminal of the signal input circuit 100 for receiving an input work mode signal. The input terminals of the work mode signal units 111 through 11J are coupled to multiple work mode signal pins Workmode_pin[1] through Workmode_pin[J] of the chip, respectively. The output terminals of the work mode signal units 111 through 11J output work mode signals Workmode_sig[1] through Workmode_sig[J] which are received from the work mode signal pins Workmode_pin[1] through Workmode_pin[J] of the chip, respectively. The input terminals of the functional signal units 121 through 12K are used as functional signal input terminals of the signal input circuit 100 and coupled to multiple functional signal pins Function_pin[1] to Function_pin[K] of the chip, respectively. The output terminals of the functional signal units 121 through 12K output functional signals Function_sig[1] to Function_sig[K] which are received from the functional signal pins Function_pin[1] to Function_pin[K], respectively. Conventionally, the signal unit is implemented by a flip-flop. As shown in FIG. 1, each work mode signal unit and each functional signal unit both include a flip-flop.
In operation, the work mode of the chip will not be changed while the chip is operating in a work mode, which means that the work mode signal is used to determine the work mode of the chip only when the chip is powered on, and the work mode signal is not changed thereafter. However, the signal from the work mode signal pin of the chip may be changed for some reasons, and the changed work mode signal can be output through the flip-flop in the work mode signal unit. Thus, the work mode of the chip will be changed. This situation should not be expected when the chip has operated in one work mode. In addition, by using the conventional signal input circuit shown in FIG. 1, each work mode signal of the chip requires a pin. Thus, pins are not efficiently used, especially in situations where the chip does not contain enough pins.